Vibrio vulnificus is a natural inhabitant of coastal waters, including the US Gulf. The bacterium causes rapid septicemia after consumption of contaminated seafood (especially raw oysters), predominantly in persons with liver dysfunction. Among food-bourne pathogens, V. vulnificus is most notable for its high rates of hospitalization and death. Indeed, V. vulnificus accounts for 1% of deaths from food-bourne illness despite causing only 0.003% of illnesses. Although infections are rare, the number of serious infections has been increasing in recent years, possibly due to global warming that has caused a rise in the number of days amenable to growth of V. vulnificus in coastal waters. Attempts by the FDA to protect consumers by implementation of post-harvest processing mandates met with significant resistance from the shellfish harvesting industry forcing the FDA to review its policies. Thus, the study of V. vulnificus pathogenesis has become a food safety and public policy priority. Recent studies establish that cytotoxicity of V. vulnificus is predominantly associated with a large Multifunctional-Autoprocessing RTX toxin (MARTXVv). In this study, we demonstrate that this toxin is directly linked to pathogenesis by the intragastric route of infection, although its targets in vivo and molecular mechanism of action remain unknown. We propose to study the role of the MARTXVv toxin in pathogenesis using in vivo, cell culture, and biochemical systems. The focus of the proposal will be mechanisms directly impacting disease due to consumption of contaminated food and identification and characterization of specific regions of the toxin linked to cell lysis and increased virulence potential.